As photoconductive compositions to be incorporated in electrophotographic photoreceptors there have heretofore been well known inorganic substances such as selenium, cadmium sulfide, zinc oxide and amorphous silicon. These inorganic substances are advantageous in that they have excellent electrophotographic properties. In particular, these inorganic substances exhibit an extremely excellent photoconductivity, charge acceptability in a dark place and insulating properties. On the contrary, however, these inorganic substances have ,various disadvantages. For example, selenium photoreceptors are expensive to manufacture, have no flexibility and cannot withstand thermal or mechanical shock. Cadmium sulfide photoreceptors can cause a pollution problem because cadmium is a toxic substance. Zinc oxide is disadvantageous in that it exhibits a poor image stability after repeated use. Furthermore, amorphous silicon photoreceptors are extremely expensive to manufacture and also require a special surface treatment to prevent surface deterioration thereof.
In recent years, electrophotographic photoreceptors comprising various organic substances have been proposed and some of them have been put into practical us to eliminate the disadvantages of inorganic substances. Examples of these approaches include electrophotographic photoreceptors comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorenone-9-one as disclosed in U.S. Pat. No. 3,484,237, electrophotographic photoreceptors comprising poly-N-vinylcarbazole sensitized with a pyrilium salt dye as disclosed in JP-B-48-25658 (the term "JP-B" a used herein means a "published examined Japanese patent application"), and electrophotographic photoreceptors comprising as a main component a eutectic complex of a dye and a resin a disclosed in JP-A-47-10375 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Furthermore, many active studies and proposals have recently been made with regard to electrophotographic photoreceptors comprising as main components organic pigments such as perylene pigment (as disclosed in U.S. Pat. No. 3,371,884), phthalocyanine pigment (as disclosed in U.S. Pat. Nos. 3,397,086 and 4,666,802), azulenium salt pigment (as disclosed in JP-A-59-53850 and JP-A-59-212542), squalium salt pigment (as disclosed in U.S. Pat. Nos. 4,396,610 and 4,644,082) and polycyclic quinone pigment (as disclosed in JP-A-59-84348 and JP-A-62-28738) or the following azo pigments:
Bisazo pigments as disclosed in JP-A-47-37543, JP-A-56-116039, JP-A-58-123541, JP-A-61-260250, JP-A-61-28453, JP-A-61-275849, JP-A-61-275850, JP-A-53-133445, JP-A-59-78356, JP-A-59-128547, JP-A-60-452453, JP-A-61-7150, JP-A-62-251752, JP-A-62-273545, JP-A-64-13555, and JP-A-64-79753, JP-B-60-5941, JP-B-60-45664, and JP-B-63-18740, and U.S. Pat. No. 4,504,559;
Trisazo pigments as disclosed in U.S. Pat. Nos. 4,436,800 and 4,439,506, and JP-A-53-132347, JP-A-55-9148, JP-A-57-195767, JP-A-57-200045, JP-A-57-204556, JP-A-58-31340, JP-A-58-31341, JP-A-58-154560, JP-A-58-60358, JP-A-58-160359, JP-A-59-127044, JP-A-59-196366, JP-A-59-204046, JP-A-59-204841, JP-A-59-218454, JP-A-60-11249, JP-A-60-111250, JP-A-61-11754, JP-A-61-22346, JP-A-61-35451, JP-A-61-67865, JP-A-61-121059, JP-A-61-63969, JP-A-61-179746, JP-A-61-230157, JP-A-61-251862, JP-A-61-251865, JP-A-61-269164, JP-A-62-21157, JP-A-62-78563 and JP-A-62-115452, and JP-B-62-39626, and JP-B-3-10419; and
Tetrakisazo pigments as disclosed in U.S. Pat. No. 4,447,513, and JP-A-60-108857, JP-A-60-108858, JP-A-60-11247, JP-A-60-111248, JP-A-60-118843, JP-A-60-176046, JP-A-61-103157, JP-A-61-117559, JP-A-61-182051, JP-A-61-94447, JP-A-61-196253, JP-A-61-212848, JP-A-61-240246, JP-A-61-273548, JP-A-61-284769, JP-A-62-18565, JP-A-62-8566 and JP-A-62-19875.
These electrophotographic photoreceptors can attain some improvement in mechanical properties and flexibility in comparison with the above described inorganic electrophotographic photoreceptors. However, these electrophotographic photoreceptors leave to be desired in sensitivity. These electrophotographic photoreceptors are also disadvantageous in that they may exhibit some change in electrical properties upon repeated use. Thus, these electrophotographic photoreceptors don't necessarily satisfy the requirements for electrophotographic photoreceptors.